Set in the 1920s, Haikara-san ga Tooru is the story of the high-spirited tomboy Benio and her relationship with a handsome half-German soldier named Shinobu. Benio is a very outgoing and athletic girl with firm ideas about being able to live her life as she wants to. When she first meets Shinobu, she dislikes him intensely, even though he manages to help her out of a series of embarrassing mishaps. She is therefore surprised when she finds out that she has been forced into an arranged marriage and that her husband-to-be is none other than Shinobu! The story then has many twists and turns, as Shinobu has to fight in the war, Benio has to wrangle with the idea of getting married, and getting along with her future in-laws and employer. Meanwhile, the great Kanto earthquake looms in the future...